1. Field of the Invention
The present invention relates to an apparatus and method for generating electron beam and, more particularly, to femtosecond electron beam generating apparatus and method capable of generating femtosecond electron beam.
2. Description of the Related Art
As the scientific technology is advancing, an electron gun is used to detect chemical or physical properties of objects. The electron gun, which refers to a device for generating electrons in the form of fine beams, is employed for electron microscopes, traveling-wave tubes, Braun tubes, cyclotrons, and the like, to detect the characteristics of target objects.
The related art electron gun generally accelerates electrons generated from a cathode by using a grid, allows the electrons to pass through a pinhole formed at an anode, and concentrates the electrons which have passed through the pinhole by using a magnetic lens or the like to generate electron beams.
However, concentration and acceleration of the electrons by using the grid, magnetic lens, or the like, lead to an increase in the length of the electron gun due to the lengths of the grid, the magnetic lens, or the like. The increase in the length of the electron gun lengthens the distance between the cathode and a sample, which disadvantageously results in elongation (i.e., time duration: pulse length or pulse width) of electron beam due to a space charge effect.
The magnetic lens has problems in that it can hardly supply stably such current as to generate high quality electron beam, it needs cooling water for its cooling, and it has an intrinsic optical aberration, or the like, complicating the fabrication of an electron gun, and making it difficult to generate high quality electron beam.
With such problems, the related art electron gun generates electron beam with a duration of picosecond (10−12), but not femtosecond electron beam. Thus, in order to detect the characteristics of various materials, an apparatus and method for generating electron beams with a duration of femtosecond (10−15) is required.